1. Field of the Invention.
This invention relates to spinnerets for the melt extrusion of synthetic polymers to produce fibers and products made therefrom and more specifically to spinnerets for the melt extrusion of synthetic polymers to produce industrial polyester fibers and products made therefrom.
2. Description of Related Art.
Industrial (i.e., high strength) fibers and multifilament yarns are well-known, including yarns comprising polyester. Such yarns have been manufactured and used commercially for more than 30 years.
Industrial polyester fibers are typically made from poly(ethylene terephthalate) polymer having a relative viscosity of about 24 to about 42, a denier per filament (dpf) of about 4 to about 8, and a tenacity of about 6.5 grams/denier to about 9.2 grams/denier. These characteristics of relative viscosity, denier and tenacity distinguish, in part, yarns described as having "industrial properties" from polyester apparel yarns of lower relative viscosity and lower denier and consequently of significantly lower strength (i.e., tenacity). Industrial polyester yarns having these properties, and processes for producing the yarns, are disclosed in U.S. Pat. No. 3,216,187 to Chantry et al.
It is also known to prepare industrial polyester yarns of varied shrinkage by a continuous process involving spinning, hot-drawing, heat-relaxing, interlacing and winding the yarn to form a package in a coupled process. U.S. Pat. No. 4,003,974 to Chantry et al. disclose such a coupled continuous process for making polyethylene terephthalate multifilament yarns having a maximum dry heat shrinkage of 4% and an elongation to break in the range of 12% to 20%. Combined with the relative viscosity, denier range and tenacity cited above, these shrinkage and elongation to break properties comprise the distinguishing features of yarns with "industrial properties".
U.S. Pat. No. 4,622,187 to Palmer discloses a continuous coupled-process for making polyester yarns of very low shrinkage of about 2%, with other properties suitable for industrial multifilament yarn applications.
Each of the Patents cited above disclose filaments, or multifilament yarns made of filaments, having circular cross-sections normal to their longitudinal axes. For use in apparel applications, it has been proposed to use fibers having non circular cross sections with lower strength than needed for industrial applications. However, to date, all commercial industrial fibers have circular cross sections. In fact, the inventors know of no prior art disclosing an industrial polyester multifilament yarn having a multifilament yarn denier range of about 600 to about 2000 with filaments other than round cross-section.
It is an object of this invention to provide spinnerets for producing industrial fibers which in turn can be made into multifilament industrial yarns and fabrics with improved cover power which reduce the weight of a fabric made from the yarns per unit area without significantly reducing the industrial properties thereof.
These and other objects of the invention will be clear from the following description.